The present invention pertains generally to ophthalmic surgery and diagnosis, particularly for identification and/or correction of optical vision deficiencies. In exemplary embodiments, the present invention provides systems and methods for planning and implementing refractive corrections in an eye of a patient, with the corrections optionally being performed using lasers.
Corneal shape corrective surgeries are commonly used to treat myopia, hyperopia, astigmatism, and the like. Laser refractive procedures include LASIK and (Laser Assisted In-Situ Keratomileusis), Photorefractive Keratectomy (PRK), Epithelial Keratomileusis (LASEK or Epi-LASEK), Laser Thermal Keratoplasty, and the Alternative refraction altering procedures which do not rely on lasers, and/or which do not alter the corneal shape, have also been described.
During LASIK, a surgeon makes a cut part way through a front surface of a cornea, optionally using an oscillating steel blade or microkeratome. The microkeratome automatically advances the blade through the cornea so as to create a thin flap of clear tissue on the front central portion of the eye. The flap can be folded over to expose stromal tissue for selective ablation with an excimer laser. More recently, femtosecond laser systems have been developed to form laser incision in the corneal tissue so as to cut the corneal flap without use of a mechanical blade. Regardless, the excimer laser is programmed to correct a visual defect by directing a beam of pulsed laser energy onto the exposed stroma. Each pulse removes a very small and precise amount of corneal tissue so that the total removal of stromal tissue from within the cornea alters and corrects the refractive properties of the overall eye. After removal (and more specifically, after laser ablation) of the desired stromal tissue, the flap can be folded back over the ablated surface. The flap of protective epithelial tissue quickly and naturally reattaches over the resculpted stromal tissue, and the eye retains much of the effective alteration in shape after corneal healing.
A number of alternative laser refractive procedures have been used and/or are being developed. In one variation, rather than incising the corneal tissue for temporary displacement of an epithelial flap, the epithelium may be ablated (typically using the excimer laser) or abraded in a PRK procedure. As an alternative to resculpting the stroma using an excimer laser, it has also been proposed to form incisions within the cornea or other refractive tissues of the eye with the femtosecond laser. Still further alternatives have been described, and new procedures are being developed to further enhance the capabilities of refractive corrections using lasers and other refractive tissue altering tools.
Known corneal correction treatment methods have generally been quite successful in correcting standard vision errors, such as myopia, hyperopia, and astigmatism. However, as with all successes, still further improvements have become desirable. Toward that end, wavefront measurement systems are now available to measure the refractive characteristics of a particular patient's eye. These wavefront measurement systems allow accurate diagnosis of the overall aberrations of the optical system of the eye, providing quite detailed information on the high-order optical aberrations that may limit a patient's visual acuity even after the standard refractive errors have been corrected (for example, by eye glasses, contact lenses, and the like). Still additional diagnostic tools may provide information which is useful for such customized ablation procedures. For example, corneal topographers are commercially available that can provide quite accurate information regarding the shape of the anterior surface of the cornea, and this surface may have a significant role in the overall optical properties of the eye. Optical coherence tomographers (OCT) may provide information regarding both the anterior and interior surfaces of the eye. By combining these accurate diagnostic tools with the flexibility of modern scanning excimer lasers, custom refractive corrections should correct not only the standard refractive errors of the eye, but also address the specific high-order aberrations of a particular patient.
Although customized laser and other refractive treatments have provided significant benefits for many patients, the overall improvement in refractive performance of the eyes of patients treated using these new techniques has not yet achieved their full theoretical potential. A number of theories or factors have been proposed to help explain why some customized ablation procedures have not altogether eliminated high-order aberrations of the eye. Even when laser refractive corrections were limited to the standard refractive errors of myopia, hyperopia, and astigmatism, the empirical response of prior treatments led to doctors applying discrete adjustment factors or “nomograms” so as to adjust a calculated prescription before imposing the treatment on an eye of a patient. Significant efforts have gone toward increasing the benefit of both standard and customized refractive corrections by identifying analogous nomogram adjustments for high-order aberration corrections. Unfortunately, work in connection with the present invention indicates the challenges of identifying suitable nomogram adjustments for a customized refractive correction for a particular patient in a particular treatment setting may continue to limit the benefits of customized corneal ablations to significantly less than the ideal potential outcomes. In fact, a significant number of high-order refractive treatments may result in other high-order aberrations of the eye actually increasing (even where the visual acuity of the eye overall benefits from the treatment).
In light of the above, it would be beneficial to provide improved devices, systems, and methods for diagnosing and/or treating refractive defects of an eye of a patient. Preferably, these improved techniques would still allow physicians to input nomogram adjustments for a particular patient. It would be particularly beneficial if these improvements were able to increase the overall accuracy with which high-order aberrations of an eye could be treated, ideally without significantly increasing the cost or complexity of diagnostic and/or treatment systems.